For Us to See Interference Phenomena in a Thin Film

Multiple Choice

For us to see interference phenomena in a thin film,

A) the incoming light must be monochromatic.
B) the index of refraction of the thin film must be greater than the index of refraction of the material below it.
C) the index of refraction of the thin film must be less than the index of refraction of the material below it.
D) the incoming light must be multicolored.
E) none of these conditions need exist